Underwater electrical cables cause major problems when they begin to leak. One of the greatest sources of leakage is in the end terminations, or "plugs". The primary water sealing means in an underwater cable should be the insulation encapsulating the strands of the individual conductors. Oftentimes the art considers the outer jacket of the bundle of conductors to be the primary sealing means, but it is actually a secondary sealing means. The major problem is that it is difficult to effect a seal between the insulating material and the plug. One of the best insulating materials for the conductors is an ethylene-propylene copolymer which does not readily bond to other sealing materials. Even commonly used epoxy pottings do not readily bond to it. One good solution to this sealing problem is to use a rubber "boot" which seals along the outside of the multiple insulated conductors and the plug body containing solder pins. Silicone grease is applied to the boot cavity after soldering the conductors to the pins, effectively sealing the area from water intrusion. In this connection, reference may be had to the field installable and testable connectors of Kintec, Inc. Such connectors work well, but are bulky, stiff, heavy and expensive. Additionally, such connectors work best for deep subsea application where the best seals are hydrostatically pressure energized. Other smaller and more flexible plugs which do not use such a boot for sealing, instead use an epoxy potting material to seal the joint. The problem with this plug is that epoxies tend to contract upon curing, leaving a channel for water to seep in, particularly if the connection is subject to cyclic flexing.
In marine seismic exploration operations, underwater electrical plugs are needed to connect power and instrumentation conductors to air guns. These guns are used as a source to obtain acoustic reflections from the seafloor. Typically, these guns are fired every 10 to 15 seconds and the impulsive pressure waves produced are quite strong. Electrical "jumper" cables used for this application must withstand a great deal of structural abuse, and normally they do not last long before developing leaks. The first-mentioned booted plug is too stiff and massive to have reasonable structural integrity to withstand such cyclic impulsive loadings. Typically, structural elements exposed to such blast elements will not last long if they are not flexible. Further, the pressure waves produced by the guns have negative (vacuum) parts, making the boots "pump". There is consequently a greater possibility that water will intrude the boot during fluctuating pressure then during static hydrostatic pressure.
Accordingly, it is the primary purpose of the invention disclosed hereinafter to provide an end terminal for an underwater electrical cable which solves these problems and which can be utilized in marine seismic operations as underwater electrical plugs which are needed to connect power and instrumentation conductors to air guns. Another purpose of the present invention is to improve the inner boot sealing capability of the end terminal, to make the connection more flexible, and to attenuate pressure loadings on the insulated conductors.
Other purposes, advantages and features of the invention will be apparent to one skilled in the art upon reviewing the following disclosure.
Applicant is not aware of any prior art references which, in his judgment as one skilled in the art of marine seismic underwater electrical plugs, would anticipate or render obvious the novel end terminal of the instant invention; however, for the purposes of fully developing the background of the invention and establishing the state of the requisite art, the following references are set forth: two diagrams of plugs available from KINTEC, Inc., 9540 Cozycroft Avenue, Chatsworth, Calif. 91311, showing respectively, FITA and MLD LP series CR plugs; U.S. Pat. Nos. 3,096,134; 3,113,999; 3,124,405; 3,158,420; 3,278,885; 3,324,449; 3,339,632; 3,410,950; 3,430,187; 3,432,612; 3,487,353; 3,489,987; 3,522,576; 3,537,062; 3,546,657; 3,665,368; 3,821,690; 3,725,846; 3,725,852; 3,729,699; 3,816,641; and 3,784,959.